On a different note, is there any special reason why you're making an array of all the users as you go? If not, you might want to consider making use of the getpw* family of functions, particularly getpwent...

#!/usr/bin/perl -w

use strict;

$|++; # disable buffering

while ( my $user = getpwent ) {
    print "\n\n", "=" x 40, "\n$user\n";
    system "/usr/bin/su", $user, "-c", "/cronme"; 
}
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    --k.